1. Field of the Invention
The present invention relates to a semiconductor device comprising a circuit structured with a thin film transistor (hereinafter referred to as TFT) formed on a substrate having an insulating surface, and also relates to a structure of a terminal for connecting the circuit structured with the TFT to a circuit on another substrate. More particularly, the present invention provides a technique suitable for use in a liquid crystal display device having a pixel portion and a driver circuit provided in the periphery of the pixel portion on the same substrate, an electro-luminescence display device, and electronic equipment mounted with an electro-optical device incorporating the above display devices. Note that in the present specification, the semiconductor device indicates general devices that may function by use of semiconductor characteristics, and that not only the above liquid crystal display device, but also the above electronic equipment incorporating the display device are categorized as the semiconductor device.
2. Description of the Related Art
In the electro-optical device, typically an active matrix type liquid crystal display device, a technique in which a TFT is utilized for the purpose of structuring a switching element and an active circuit has been developed. A TFT is formed with a semiconductor film as an active layer formed on a substrate such as a glass substrate by vapor phase growth. A material such as silicon or silicon germanium having silicon as its principal constituent is suitably utilized for the semiconductor film. In addition, an amorphous silicon film or a crystalline silicon film typically such as a polycrystalline silicon film can be obtained depending on the manufacturing method of the silicon semiconductor film.
The TFT using the amorphous silicon film as the active layer essentially cannot attain an electric field effect mobility of several cm2/Vsec or more because of electronic properties caused by the amorphous structure, or the like. Accordingly, despite being able to utilize the TFT as the switching element (pixel TFT) for driving the liquid crystals provided in each pixel in the pixel portion, it is impossible to form the TFT up to a point as a driver circuit for performing image display. In order to provide a driver circuit for performing image display, a technique in which a driver IC is mounted by the TAB (Tape Automated Bonding) method or the COG (Chip On Glass) method has been employed.
On the other hand, with the TFT using the crystalline silicon film as the active layer, it is possible to attain a high electric field effect mobility to form various functional circuits on the same glass substrate. Besides the pixel TFT, in the driver circuit, circuits basically formed of a CMOS circuit consisting of an n-channel TFT and a p-channel TFT, such as a shift resistor circuit, a level shifter circuit, a buffer circuit, and a sampling circuit, can be manufactured on the same substrate. An active matrix substrate having the pixel and the driver circuit for driving the pixel formed on the same substrate is utilized in the active matrix type liquid crystal display device for the purpose of reducing cost and improving quality.
In the active matrix substrate such as the above, in order to supply electric power and an input signal to the driver circuit, a connecting wiring connected to the driver circuit is formed on the active matrix substrate. A structure mounted with the connecting wiring and an FPC (Flexible Print Circuit) is being adopted. An anisotropic conductive film is used for the connection of the connecting wiring and the FPC on the substrate. FIG. 30 shows a sectional structure of the connecting wiring connected to the FPC by means of the anisotropic conductive film.
As shown in FIG. 30, in the active matrix substrate, a connecting wiring 3 is formed on an insulating film 2 that is on the surface of a glass substrate 1. The FPC 4 includes a substrate 5 made of a flexible material such as polyimide, and a plurality of wiring 6 made of copper etc. are formed thereon. In an anisotropic conductive film 7, conductive spacers 8 are dispersed into an adhesive 9 (resin) that cures from heat or light. The connecting wiring 3 is electrically connected to a wiring 6 on the FPC 4 by a conductive spacer 8.
The connecting wiring 3 is a two multi-layer structure consisting of a metallic film 3a such as aluminum and titanium and a transparent conductive film 3b such as an ITO film. Since the transparent conductive film 3b utilizes a metallic film such as aluminum, its wiring resistance can be lowered. Hence, there is fear that the metallic film 3a may be deformed due to being pressed by a conductive spacer 8. The transparent conductive film 3b is made of metal oxide such as indium and tin, thus its degree of hardness is higher than the metallic film 3a. Accordingly, the transparent conductive film 3b is formed on the surface of the metallic film, preventing the metallic film 3a from being damaged or deformed.
Nonetheless, a side surface of the metallic film 3a is in an uncovered state, and exposed to air until an anisotropic conductive film 7 is formed. The metallic film 3a is under a state easily exposed to corrosion and oxidation, the cause of lowering the connection reliability of the connecting wiring 3 and the FPC 4. Furthermore, the side surface of the metallic film 3a is touching the resin in a state where the FPC 4 is mounted, causing a problem in protecting against moisture.